---
title: "Short notes on branches of metrology"
subject: "Metrology"
chapter: 1
key: "semester_3/metrology:legal-dynamic-deterministic-metrology"
source: https://www.bctengineer.com/q/semester_3/metrology/legal-dynamic-deterministic-metrology
site: BCT Engineering
---

# Short notes on branches of metrology

Metrology · Chapter 1: Introduction to Metrology

- Asked in: year not given, 6 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/metrology/legal-dynamic-deterministic-metrology
- Whole chapter: https://www.bctengineer.com/md/semester_3/metrology/chapter-1

## Question

Write short notes on: (a) legal metrology, (b) dynamic metrology, (c) deterministic metrology. Also list the seven SI base units with their symbols.

## Short answer

Legal metrology: measurements regulated by law for trade and safety, with mandatory verification. Dynamic metrology: fast-changing quantity measurement using rapid instruments for continuous recording. Deterministic metrology: predicts and corrects errors via model, used in high-accuracy automated metrology. SI base units: metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), candela (cd).

## Answer

#### Legal metrology
It deals with the units of measurement, the measuring instruments and the methods of measurement that are covered by law, to protect the public in trade, health, safety and the environment. Examples are weighing scales in shops, petrol pump meters, electricity meters and taxi meters. A government body verifies, stamps and periodically re-inspects such instruments, and the use of unfair or inaccurate instruments is penalised.

#### Dynamic metrology
It is the measurement of quantities that change rapidly with time, using instruments that respond fast, so that the variation of the quantity is recorded continuously rather than as one fixed value. Examples are vibration, pressure pulses in an engine cylinder, surface roughness traced while the stylus moves, and measurement of the dimensions of a component on a moving production line.

#### Deterministic metrology
Here the measurement is carried out in a fully controlled and described way, so that the result can be predicted from a mathematical model of the measuring system. Instead of relying only on repeated trials, errors are calculated and corrected (for example thermal expansion and elastic deformation of the instrument). In this approach, measurement of the process largely replaces measurement of each part. It is used in high-accuracy work such as CMMs, error-compensated CNC machines and gauge block calibration, where the part is treated as a known geometrical form and the measurement is automated.

#### SI base units

| Quantity | Unit | Symbol |
|---|---|---|
| Length | metre | m |
| Mass | kilogram | kg |
| Time | second | s |
| Electric current | ampere | A |
| Temperature | kelvin | K |
| Amount of substance | mole | mol |
| Luminous intensity | candela | cd |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Legal metrology mainly deals with instruments and measurements that are:
   A. Covered by law to protect the public in trade, health, safety and environment
   B. Used only in research laboratories
   C. Of highest possible accuracy
   D. Used only for moving parts
   Answer: A. Legal metrology covers units, instruments and methods regulated by law, e.g. shop scales and petrol pumps, to protect the public. (Key point: Purpose of legal metrology)

2. Which situation is an example of dynamic metrology?
   A. Calibrating a gauge block in a lab
   B. Checking a shop weighing scale
   C. Recording pressure pulses in an engine cylinder
   D. Measuring a stationary shaft with a vernier
   Answer: C. Dynamic metrology measures quantities that change rapidly with time, with the variation recorded continuously, like vibration or cylinder pressure pulses. (Key point: Dynamic metrology)

3. What characterises deterministic metrology?
   A. It relies only on repeated trials and averaging
   B. The result is predicted from a mathematical model, with errors calculated and corrected
   C. It is used only for legal trade
   D. It measures only rapidly changing quantities
   Answer: B. In deterministic metrology the measuring process is fully controlled and modelled, so errors such as thermal expansion are calculated and corrected. (Key point: Deterministic metrology)

4. Which pair of SI base quantity and unit symbol is correct?
   A. Temperature - C
   B. Luminous intensity - cd
   C. Amount of substance - mo
   D. Electric current - a
   Answer: B. Luminous intensity is measured in candela (cd). Temperature is kelvin (K), amount of substance mole (mol), current ampere (A). (Key point: SI base units)

## Related in Metrology

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